Injection of CO₂-Saturated Water through a Siliceous Sandstone Plug from the Hontomin Test Site (Spain): Experiment and Modeling

Abstract

Massive chemical reactions are not expected when injecting CO(2) in siliceous sandstone reservoirs, but their performance can be challenged by small-scale reactions and other processes affecting their transport properties. We have conducted a core flooding test with a quartzarenite plug of Lower Cretaceous age representative of the secondary reservoir of the Hontomín test site. The sample, confined at high pressure, was successively injected with DIW and CO(2)-saturated DIW for 49 days while monitoring geophysical, chemical, and hydrodynamic parameters. The plug experienced little change, without evidence of secondary carbonation. However, permeability increased by a factor of 4 (0.022-0.085 mD), and the V(P)/V(S) ratio, whose change is related with microcracking, rose from ~1.68 to ~1.8. Porosity also increased (7.33-8.1%) from the beginning to the end of the experiment. Fluid/rock reactions were modeled with PHREEQC-2, and they are dominated by the dissolution of Mg-calcite. Mass balances show that ~4% of the initial carbonate was consumed. The results suggest that mineral dissolution and microcracking may have acted in a synergistic way at the beginning of the acidic flooding. However, dissolution processes concentrated in pore throats can better explain the permeability enhancement observed over longer periods of time.

CO2‐induced chemo‐mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing

“…In reservoirs where the in situ stress state is lower than the yield stress, dissolution may result in porosity increase, as evidenced by this study, and therefore permeability increases . This is the case of the unstressed CO 2 ‐brine reaction experiments conducted in this study.…”

“…Alteration of rocks with CO 2 ‐brine in the laboratory also results in measurable changes in geomechanical and transport properties, such as increased permeability and porosity, dissolution of siliceous and carbonate minerals, reduction of indentation stiffness, reduction of fracture toughness, and decrease of the size of yield stress locus . Changes are more impactful in rocks with load‐bearing dissolvable minerals or clay cements sensitive to pore‐fluid chemistry …”

Experimental Perspectives of Mineral Dissolution and Precipitation due to Carbon Dioxide-Water-Rock Interactions

“…Mineral dissolution includes both direct dissolution (mainly of carbonates, e.g. Kj¿ller et al 2011;Canal et al 2013;Jun et al 2013) and hydrolysis of feldspars and phyllosilicates leading to precipitation of clays and other secondary silicate minerals (Lin et al 2008;Hangx and Spiers 2009). Precipitation of secondary carbonates is likely to take place further away, after the initial acidification of formation waters has been neutralized and silicate reactions have disturbed the initial carbonate-fluid equilibrium (Bateman et al 2010).…”

“…Canal et al (2013) measured changes in porosity due to calcite dissolution and found a marked increase in permeability and changes to seismic velocities. Bachaud et al (2011) measured increased porosity in limestone caprock; in contrast, permeability remained low in these experiments.…”

“…Experiments on natural rock cores provide a test for computer models (Canal et al 2013) and have been used to investigate trapping mechanisms (Iglauer et al 2011) and the effect of reactivity on the physical properties of reservoir rocks (Hangx et al 2010). In the event that GCS is implemented commercially, it seems likely that such measurements will be an important part of site characterisation and evaluation.…”